Thermoplastic films and sheets are used in photovoltaic (PV) module glazings as an alternative to glass. Thermoplastics offer advantages of lighter weight, as well as higher light transmittance. The thermoplastic glazing can be used on both flexible and rigid photovoltaic modules. ETFE (ethylene tetrafluoroethylene) is used currently for the manufacture of amorphous silicon cells as an upper glazing material, especially for flexible PV modules. These are sold as gloss-gloss films by commercial suppliers such as DuPont and Saint Gobain.
Polymethylmethacrylate (PMMA) glazing is also being used in PV modules. Weatherability and dirt-shedding of PMMA glazing can be improved by adding a thin polyvinylidene fluoride (PVDF) film on the outer surface, as described in U.S. 60/835,855. PVDF can also be used as a film for the front glazing of a flexible PV module, as described in U.S. 60/989,501. In all of these cited references, the thermoplastic glazing was used with a flat, gloss outer side.
There is a continued effort in the photovoltaic module industry to improve the efficiency of the module and reduce cost. Efforts have been made to use concentrators to reduce the level of silicon, and to use less quantity and less expensive materials. Different surface patterns have also been used to increase the transmittance of solar energy.
Textured surfaces have been used in photovoltaic glazing. US 2005/0039788 and US 2007/0240754 describe a textured transparent glazing having a plurality of large geometric features, which can improve the light transmission of the panel. Light transmission is increased clue to both the reduction of reflection from the textured surface, and also light reflected back to the environment after entering the glazing is reduced. The glazing having the textured surface is relatively thick—in the range of 0.5 to 10 mm. Measured light transmission was as high as 91.9 percent
US 2004/0261836 describes a solar cell having an uneven texture fluoride polymer front surface that is subjected to a discharge treatment, to improve the stain resistance. The fluoropolymer film preferably has an uneven pattern that can be applied by pressing with a cooling roll or sandblasting.
It has now been found that a thermoplastic glazing with an external matte surface transmits more solar radiation than a flat surface, or a glazing having a matte surface on the inside surface. Moreover, the matte surface can be translucent, and still transmit high levels of solar radiation. A thermoplastic glazing with a low refractive index also increases solar transmittance, and especially when in combination with a higher refractive index inner layer.